The invention concerns a process for the control of a variable, and an apparatus to carry out that process.
In a control circuit, frequently nonlinear functional parts with nonlinear characteristic curves are found. One example involves a nonlinear behavior of the measuring instrument so that the measuring signal passed to the control apparatus is no longer proportional to the control variable itself. In many cases this may be desirable, for example, for extracting the square root of a signal introduced as a control variable, and in other cases this may be taken into account by the suitable layout of the other control circuit components. There is, however, a problem if the characteristic of the measuring device is no longer monotonic in the measuring range, so that a certain measuring signal corresponds to several states of the control variable, including an unwanted state, i.e., the measuring signal no longer characterizes the control variable in an unambiguous manner. This results in the condition that the process involved is no longer controlled in a stable fashion over the entire control range by a known regulating device.
It is, therefore, an object of the invention to provide a process and an apparatus for the control of a process variable, whereby stable regulation is obtained in the simplest possible manner within a control range, in which the constant characteristic of the measuring device has an extreme value and is therefore not monotonic.